Definitions
- Ahupua'a
- Traditional unit of land in the Hawaiian Islands, extending from the ocean
to the upper mountain slopes so that the occupants could have access to
resources from both the sea and the forests.
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- Koa
- Acacia koa, a native Hawaiian forest tree found at altitudes of
450-1220 m on the mountain slopes.
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- Ohia
- Metrosideros collina, subsp. polymorpha, a tree indigenous to the Hawaiian Islands,
the dominant species in rain forests and found in other environments as well.
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- Orographic rainfall
- Orographic means 'associated with the presence of mountains'.
Orographic rainfall is rain that occurs as moist air is forced to rise by
mountain slopes. It is a common climate pattern in coastal mountains
and mountains in the trade wind latitudes.
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- Stable isotope tracers
- Water (H2O) has two elements, hydrogen and oxygen. Both
elements have stable isotopes (atoms with a different number of neutrons)
that occur naturally. The difference in mass between the isotopes
causes fractionation when the water molecules undergo physical or chemical
changes. This fractionation allows isotope ratios to be used as
tracers of hydrologic processes such as evaporation and condensation.
In our studies we use the ratios between oxygen 18/oxygen 16, and
deuterium/hydrogen, as hydrologic tracers. Most of the Hawaii studies are based on the fact that rain falling at
different altitudes and in different microclimates on the mountain slopes
has distinct variations in isotopic composition, allowing sources of
surface- and ground water to be determined. Much more information can
be found at the International Atomic Energy Agency (IAEA)
isotope hydrology Web site.
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- Throughfall
- Precipitation that has fallen through vegetative canopy, including rain or
fog that collects on leaves and branches.
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- Water budget
- An assessment of all the inputs and outputs to a hydrologic system.
Budget components might include, for example, rain and fog as
inputs, soil water as storage, and stream runoff and evapotranspiration as outputs. Relative
proportions of the different water budget components are either measured or
estimated, so that gains are balanced with storage and losses from the
system.
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